1. Field of the Invention
The embodiments of the invention generally relate to integrated circuit structures and, more specifically, to integrated circuit transistor structures that include multiple body doping regions having different depth profiles.
2. Description of the Related Art
In conventional systems for changing threshold voltage of a transistor on a chip, the semiconductor body of the transistor can be doped with dopants by ion implantation. Control of the value of the threshold voltage is critical to good performance and low power consumption of the circuits employing the transistors. For many applications it would be desirable to control the body potential. This may usually be accomplished by changing the transistor layout to include a body contact region at the surface, which electrically connects to the body through the device width direction.
A metal oxide semiconductor field effect transistor (MOSFET) has four terminals, source, drain, gate and body/substrate. Body potential is typically ground, but can be changed. The change in body potential leads to a MOSFET threshold voltage change and this phenomenon is referred to as “body effect”, or substrate effect. The amount of threshold voltage change for a certain body potential change is the body sensitivity.
The body effect describes the changes in the threshold voltage by the change in the source-bulk voltage, approximated by t:VTN=VTO+γ(√{square root over (VSB+2φ)})
VTN is the threshold voltage with substrate bias present, VTO is the zero-VSB value of threshold voltage, γ is the effect parameter, and 2φ is the surface potential parameter. The body can be operated as a second gate, and is sometimes referred to as the “back gate.” The body effect is sometimes referred to as the “back-gate effect.”